FreeBSD is in need of a new linux_base port. It is on my TODO list since a long time, but I do not get the time to cre­ate one. I still do not have the time to work on a new one, but when you read this, I man­aged to get the time to cre­ate a HOWTO which describes what needs to be done to cre­ate a new linux_base port.

I will not describe how to cre­ate a new linux_base port from scratch, I will just describe how you can copy the last one and update it to some­thing newer based upon the exist­ing infra­struc­ture for RPM packages.

Spe­cific ques­tions which come up dur­ing port­ing a new Linux release should be asked on freebsd-emulation@FreeBSD.org, there are more peo­ple which can answer ques­tions than here in my blog. I will add use­ful infor­ma­tion to this HOWTO if necessary.

In the easy case most of the work is search­ing the right RPMs and their depen­den­cies to use, and to cre­ate the plist.

Why do we need a new linux_base port?

The cur­rent linux_base port is based upon Fedora 10, which is end of life since Decem­ber 2009. Even Fedora 13 is already end of life. Fedora 16 is sup­posed to be released this year. From a sup­port point of view, Fedora 15 or maybe even Fedora 16 would be a good tar­get for the next linux_base port. Other alter­na­tives would be to use an extended life­time release of another RPM based dis­tri­b­u­tion, like for exam­ple Cen­tOS 6 (which seems to be based upon Fedora 12 with back­ports from Fedora 13 and 14). Using a Linux release which is told to be sup­ported for at least 10 years, sounds nice from a FreeBSD point of view (only minor changes to the linux ports in such a case, instead of cre­at­ing a com­plete new linux_base each N+2 releases like with Fedora), but it also means addi­tional work if you want to cre­ate the first linux_base port for it.

The mys­ter­ies you have to con­quer if you want to cre­ate a new linux_base port

What we do not know is, if Fedora 15/16, Cen­tOS 6, or any other Linux release will work in a sup­ported FreeBSD release. There are two ways to find this out.

The first one is to take an exist­ing Linux sys­tem, chroot into it (either via NFS or after mak­ing a copy into a direc­tory of a FreeBSD sys­tem), and to run a lot of pro­grams (acroread, skype, shells, scripts, …). The LTP test­suite is not that much use­ful here, as it will test mostly ker­nel fea­tures, but we do not know which ker­nel fea­tures are manda­tory for a given user­land of a Linux release.

The sec­ond way of test­ing if a given Linux release works on FreeBSD is to actu­ally cre­ate a new linux_base port for it and test it with­out chrooting.

The first way is faster, if you are only inter­ested in test­ing if some­thing works. The sec­ond way pro­vides an easy to setup test­bed for FreeBSD ker­nel devel­op­ers to fix the Lin­ux­u­la­tor so that it works with the new linux_base port. Both ways have their mer­its, but it is up to the per­son doing the work to decide which way to go.

The meat: HOWTO cre­ate a new linux_base port

First off, you need a sys­tem (or a jail) with­out any linux_base port installed. After that you can cre­ate a new linux_base port (= lbN), by just mak­ing a copy of the lat­est one (= lbO). In lbN you need to add lbO as a CONFLICT, and in all other exist­ing linux_base ports, you need to add lbN as a conflict.

Change the PORTNAME, PORTVERSION, reset the PORTREVISION in lbN, and set LINUX_DIST_VER to the new Linux-release ver­sion in the lbN Make­file (this is used in PORTSDIR/Mk/bsd.linux-rpm.mk and PORTSDIR/Mk/bsd.linux-apps.mk).

If you do not stay with Fedora, there is some more work to do before you can have a look at chos­ing RPMs for instal­la­tion. You need to have a look at PORTSDIR/Mk/bsd.linux-rpm.mk and add some cases for the new LINUX_DIST you want to use. Do not for­get to set LINUX_DIST in the lbN Make­file to the name of the dis­tri­b­u­tion you use. You also need to aug­ment the LINUX_DIST_VER check in PORTSDIR/Mk/bsd.linux-rpm.mk with some LINUX_DIST con­di­tion­als. If you are lucky, the direc­tory struc­ture for down­loads is sim­i­lar to the Fedora struc­ture, and there is not a lot to do here.

When this is done, you can have a look at the BIN_DISTFILES vari­able in the lbN Make­file. Try to find sim­i­lar RPMs for the new Linux release you want to port. Some may not be avail­able, and it may also be the case that dif­fer­ent ones are needed instead. I sug­gest to first work with the ones which are avail­able (make make­sum, test install and cre­ate plist). After that you need to find out what the replace­ment RPMs for non-existing ones are. You are on your own here. Search around the net, and/or have a look at the depen­den­cies in the RPMs of lbO to deter­mine if some­thing was added as a depen­dency of some­thing else or not (if not, for­get about it ATM). When you man­aged to find replace­ment RPMs, you can now have a look at the depen­den­cies of the RPMs in lbN. Do not add blindly all depen­den­cies, not all are needed in FreeBSD (the linux_base ports are not sup­posed to cre­ate an envi­ron­ment which you can chroot into, they are sup­posed to aug­ment the FreeBSD sys­tem to be able to run Linux pro­grams in ports like they where FreeBSD native pro­grams). What you need in the linux_base ports are libraries, con­fig and data files which do not exist in FreeBSD or have a dif­fer­ent syn­tax than in FreeBSD (those con­fig or data files which are just in a dif­fer­ent place, can be sym­linked), and basic shell com­mands (which com­mands are needed or not… well… good ques­tion, in the past we made deci­sions what to include based upon prob­lem reports from users). Now for the things which are not avail­able and where not added as a depen­dency. Those are things which are either used dur­ing install, or where use­ful to have in the past. Find out by what it was replaced and have a look if this replace­ment can eas­ily be used instead. If it can be used, add it. If not, well… bad luck, we (the FreeBSD com­mu­nity) will see how to han­dle this somehow.

If you think that you have all you need in BIN_DISTFILES, please update SRC_DISTFILES accord­ingly and gen­er­ate the dis­t­file via make –DPACKAGE_BUILDING make­sum to have the check­sums of the sources (for legal rea­sons we need them on our mirrors).

The next step is to have a look at REMOVE_DIRS, REMOVE_FILES and ADD_DIRS if some­thing needs to be mod­i­fied. Most of them are there to fall back to the cor­re­spond­ing FreeBSD directories/files, or because they are not needed at all (REMOVE_*). Do not remove direc­to­ries from ADD_DIRS, they are cre­ated here to fix some edge con­di­tions (I do not remem­ber exactly why we had to add them, and I do not take the time ATM to search in the CVS history).

If you are lucky, this is all (make sure the plist is cor­rect). If you are not lucky and you need to make some mod­i­fi­ca­tions to files, have a look at the do-build tar­get in the Make­file, this is the place where some changes are done to cre­ate a nice user experience.

If you arrive here while cre­at­ing a new linux_base port, lean back and feel a bit proud. You man­aged to cre­ate a new linux_base port. It is not very well tested at this moment, and it is far from every­thing which needs to be done to have the com­plete Linux infra­struc­ture for a given Linux release, but the most impor­tant part is done. Please notify freebsd-emulation@FreeBSD.org and call for testers.

What is missing?

The full Lin­ux­u­la­tor infra­struc­ture for the FreeBSD Ports Col­lec­tion has some more ports around a linux_base port. Most of the infra­struc­ture for this is han­dled in Mk/bsd.linux-apps.mk.

Fedora 15/16 are increas­ingly inte­grated with sys­temd which seems to pro­vide much more func­tion­al­ity than just ser­vice man­age­ment. Have you actu­ally tried whether Fedora 16 still works in a chroot?

As in the “The mys­ter­ies you have to con­quer if you want to cre­ate a new linux_base port” part explained: no, I have not tested any Linux-release, so I do not know if Fedora 15/16 will work or not.

As the linux_base port is not a com­plete Linux user­land, and we need only parts of it to have Skype, acroread and other soft­ware work­ing, it is still unknown to me if the use of sys­temd in Fedora 15/16 is a show­stop­per or not.